Utilization of foul steam for hydrogen sulphide removal



Dec. 14, 1943. w. H. SHIFFLERIET AL 6,896

UTILIZATION OF FOUL STEAM FOR HYDROGEN SULPHIDE REMOVAL Original Filed Dec. 9. 1940 H25 HZS-FREE ABSORPTION I HYDRO- MEDIUM CARBONS MIXING SEPARATION R s H,

, H 2 s A I STEAM II s- IcII I H MUCH -ABsoRPTIoN SYDRO- V A MED'UM CARBQNS A REGENERATED ABSORPTION MED UM R s H ABSORPTION RS H RICH REGENERATED MEDIUM I ABSORPTION ABSORPTION MEDIUM MEDIUM M\XING SEPARATION RSH-FREE RSH-RICH HYDRO- HYDRQ- C'ARBONS. CARBONS I'NVENTORS 1447/1212 65 Shiffier By ATTORNEY Patented Dec. 14, 1943 I UNITED STATES PAT N OFFICE UTILIZATION OF FOUL STEAM FOR HY- DROGEN SULPHIDE REMOVAL William H. Shifiier, San Francisco, and Laverne P. Elliott, Berkeley, Calif., assignorsto Standard Oil Company of California, San Francisco, Calif., a corporation of Delaware ""OriginaI application December 9, 1940, Serial No.

. 369,230. Divided and this application December 16, 1942, Serial No. 469,190 I 4 Claims. (Cl. 196 30) .tomarily, the hydrogen sulphide is first removed.

- There are various methods' of removing said hydrogen sulphide, included! among which are washing with aqueous alkaline solutions, scrubbing with amine solutions, or with-potassiufn salts of phosphoric acid, such as tri-potassium phosphate or with sodium phenolate.

The remaybe re-used: This is also true in the various processes for removal of hydrogen sulphide and mercaptans from hydrocarbons. Chemicals used in the removal ofhydrogen sulphide and mercaptans are regeneratedby steaming the spent solutions containing the removedhydrogen sulphide and mercaptans. For instance, in the removal of mercaptan by use of caustic soda the mercaptans are converted into mercaptides and the hydrolysis resulting from the subsequent steaming of the spent caustic solution.regener- Y ates the caustic and releases the mercaptans with the steam. In the removal of hydrogen. sulphide by use of tri-potassium phosphate or amine soluvtions the reaction may be represented as the ab- .sorption of hydrogen sulphide by a weak base.

Upon steaming the spent treating solution the reaction is reversed, hydrogen sulphide is given moval of hydrogensulphide with aqueous alkaline solutions has long been used and the methods of such use are familiar to those skilled in the art. The removal of hydrogen sulphide with the use of tri-potassium phosphate is describedin Proceedings of Eighth Mid-Year MeetingAmerican Petroleum Institute (vol. 19M, 1938, pages 47-53) in a paper presented by T. W. Rosebaugh. The use of sodium phenolate as the absorption medium has been described in Proceedings of Eighth Mid-Year MeetingAmerican Petroleum Institute (vol. 19M, 1938, pages 23-33). The process of using amine solutions is described in Proceedings of Eighth Mid-Year Meeting American Petroleum Institute (vol. 19M, 1938, pages 34-36) in a paper presented by Wood and Storrs. The use of aliphatic and cycloparaiiin amines has been found especially desirable.

Various methods also exist for removal of mercaptans, chief among which is scrubbing with aqueous alkaline solutions such as sodium or potassium hydroxide, with or without the aid of suitable organic solvents or organic acids which increase the solubility of the aqueous alkaline solution for the mercaptans. The removal of mercaptans by scrubbing with aqueous alkaline solutions has long been employed and the methods of such use are familiar to those skilled in the art.

In processes of chemically refining hydrocarbons, in order that the process may be economically employable, it is normally necessary to regenerate the chemicals employed so that they lution regenerated.

oil" andthe tri-potassium phosphate or amine so- In all the processes for removal of hydrogen sulphide and mercaptans involvin the regeneration' of the chemical employed-by steaming, the

"generation of the necessary steam is one Of the major items of expense. In fact,in the operation of the amine or tri-potassium phosphate hydrogen sulphide removal processes, since no chemicals are'consumed, the main item of operating expense isthe generation of the steam necessary to regenerate the spent treating solution. For instance, in aplant capable of treating approximately four and a, half million cubic-feet per day of hydrocarbon gas containin hydrogen sulphide from 3,000 to 8,000 pounds of steam per hour are required.

The steam employed in regenerating aqueous alkali solutions used for removing mercaptans fromgasoline is customarily wasted. Not only is such steam wasted, but, because it contains the removed foul-smelling mercaptans, it presents a serious disposal problem. See, for instance, the paper presented by William Medius, before the Mid-Year Meeting, American Petroleum Institute, Tulsa, Oklahoma, June 1-3, 1932, entitled Closed System Effective for Disposal of Sulfur Gases in Refinery. V

Applicants have discovered that the foul mercaptan-containing steam from the regeneration of aqueous alkali solutions used in removing mercaptans from gasoline, which is normally Wasted. can instead be employed to regenerate treating solutions used to remove hydrogen sulphide from hydrocarbons.

Contrary to what was reasonably to be ex- The process described herein.

pected, when'lthe foul mercaptan-containing steam is used to regenerate the spent solution I used to absorb-hydrogen sulphide, the spent-tripotassium phosphate solution for instance, there r I is substantially no absorption of themercaptans 3 in the hydrogen sulphide absorption medium being regenerated and there is no polluting of the hydrocarbons from which the hydrogen sulphide is being removed by the mercaptan in the steam employed.

Our invention can be described by. reference to the accompanying drawing in the form ota flow. sheet. In thelower line of flow, hydrocarbons containing mercaptans are admixed in a conventional manner with the mercaptanabsorption medium followed by conventional separation or trained mercaptans. from the hydrocarbons stripped of mercaptans. In the'upperline of flow, hydrocarbons containing hydrogen sulphide. are admixed in a conventional manner with the e the absorption medium, now containing the en-' acid to absorb at least a substantial portion of said fhydrogen sulphide in said solution after which th'ehydrogen sulphide-freed hydrocarbons are separated from the solution containing potassium salts of phosphoric acid and said absorption medium is regenerated for reuse, and employing said foul, mercaptan-containing steam from themercaptan-removal system to regen- V erate said solution containing potassium salts of hydrogensulphide absorption medium, followed by conventional separation ofthe absorptionmedium, now" containing the entrained hydrogen sulphide, from the hydrocarbons stripped of:hy-

drogen sulphide. ln'order' that the respective sorption they are regenerated by the use-of steam.

Free steam is introduced into the mercaptanrich absorption medium forsuch purpose. 1'Such regeneration step may be assisted by-the :addil 'tional use of a closed steam coil. The free steam emerging from mercaptan' absorption medium regenerator, containing the mercaptan removed from the mercaptan absorption medium, ispassed directly to the. hydrogen sulphide absorption. me-

dium reg'eneratorwhere it is employed to drive off thehydrogen' sulphide entrained in the hydrogen sulphide absorption medium an'd :thus

' regenerate the hydrogen sulphide absorption medium.= .The driving offof the entrained hydrophosphoric acid and to evolve hydrogen sulphide therefrom. i

'2. The. process comprising mixing hydrocar bons containing mercaptans with an aqueous alkaline solution in order to remove said merabsorption media may be recycled for further abcaptans from said hydrocarbons, separating said hydrocarbons thus freed of mercaptans from. 1 said aqueous alkaline solution, regenerating said aqueous alkaline solution for further use in mer captanabsorption by steaming the same, passing the foul, mercaptan containing steam to a hydrogen sulphide removal treatment wherein hydrocarbons containing hydrogen sulphide-are contacted with aliquid absorption medium for vhydrogen, sulphide comprising a solution containing tri-potassium' phosphate to absorb at least asubstantial portion'ofsaid hydrogen sulphide in said solution after which the hydrogen sulphide may be assisted-by the additional/f use of a closed steam coil. The'hydrocarbons thusfreed of mercaptans and hydrogen sulphide I may be'passed =to.storage,' recycled or otherwise treated in any desired manner. The regeneratedmercaptan. and hydrogen sulphide 'absorption mediumsare recycled for furtherabsorption of mercaptans and hydrogen sulphide. The by- -products of the process, namely thewhydrogen sulphide and themercaptans, may be put to any desired and appropriateuse, such as'the manufacture ofsulphur. or sulphuric'.acid.- The ultilization of the 'foul mercaptan-rich stearn,. whichhas heretofore been with dimculty disposed of or wasted, in'order'to regenerate the I treating solution used to remove hydrogen sulphide, constitutes a major economy in reflnery {operations directed to the removal of mercap tans and hydrogen sulphide. j 1;- i n I I is applicable to removal of hydrogen sulphide and'mercaptans from both gaseous andliquid hydrocarbons.

1 We claim: I

- l. The process comprising mixing hydrocarbons containingmercaptans with an aqueous alkaline solutionin order tocremove said mercaptans from said hydrocarbons, separating,;said

' gen sulphide-freedhydrocarbons are separated from the solution containing' tri-potassium phos- .-phate and said absorptionmedium is regenerated for reuse, and employing said foul, mercaptancontaining steam from. the mercaptan-removal' systemto regenerate saidsolution containing tripotassium phosphate and to evolve hydrogen sulphide therefrom. a

3. In a process of treating hydrocarbons to remove hydrogen sulphide by absorptionv in an alkaline liquid absorption medium capable of regeneration by steam and comprising an aqueous solution containing potassium salts of phosphoric acid, the 1 steps of removing hydrogen sulphide absorbedin said absorption medium by steaming said absorption medium with steam fouled with mercaptanspreviously extracted from hydrocar-' bons in a mercaptanabsorption step, removing both hydrogen sulphideand said mercaptans in the exhaust steam from said steaming operation,

and recycling said absorption medium to remove hydrogen sulphide from hydrocarbons substantially without introducing mercaptans therein.

. 4. A process as in claim 3,:wherein said alkaline liquid absorption medium for hydrogen sulphide is a solution containing tri-potassium phosphate. i

. WILLIAM H. SHDF'FLER. LAVERNE P. ELLIO'I'I. 

